(a) Field of the Invention
The present invention relates to a water-flowing mechanism of a wet type electrostatic precipitator, and more particularly to a water-flowing mechanism of a wet type electrostatic precipitator having plural dust-collecting plates along a flow path of gas to be treated.
(b) Description of the Related Art
From exhaust gas from a boiler using heavy oil or coal as a fuel such as a thermal power plant, dust is removed by a dry type electrostatic precipitator, then, sulfur oxides are removed by a wet desulfurizer, and finally, mist or dust remaining in the exhaust gas is removed by a wet type electrostatic precipitator.
FIG. 14 is a general view of a wet type electrostatic precipitator according to a conventional art. FIG. 14A is a perspective view, FIG. 14B is a front view seen from an inlet port 102, and FIG. 14C is a side view of FIG. 14B. A wet type electrostatic precipitator 100 shown in FIG. 14A has a casing 101 (a portion indicated by a broken line in FIG. 14A) that forms an overall shape.
The front face of the casing 101 extends outwardly in a pyramid form. The inlet port 102 from which gas to be treated 106 is introduced is formed at the leading end of the casing 101. The back face opposite to the front face similarly extends outwardly in a pyramid form, and a discharge port 103 from which treated gas 107 is discharged is formed at its leading end (see FIGS. 14B and 14C). Here, the inlet port 102 and the discharge port 103 are formed at the center of the front face and the back face respectively considering uniform dispersion of airflow. The casing 101 is supported by legs 111 at the corners of the bottom face.
On the other hand, plural plate-like dust-collecting plates 104 (the mesh portion in FIG. 14A) and plural plate-like discharge electrodes 105 are alternatively arranged in line facing in parallel to each other at equal interval. In order to allow the gas to be treated 106 to be easily vented, the dust-collecting plates 104 and the discharge electrodes 105 are arranged such that the side faces thereof are directed toward the inlet port 102 or the discharge port 103. Strong electric field is applied between the discharge electrodes 105 and the dust-collecting plates 104.
With this configuration, the gas to be treated 106 introduced from the inlet port 102 passes between the dust-collecting plates 104 and the discharge electrodes 105, and mist and dust contained in the gas to be treated 106 are charged by the discharge electrodes 105, so that the mist and dust are attracted to the dust-collecting plates 104 with coulomb force to be colleted. The gas to be treated 106 from which mist and dust are removed is discharged from the discharge port 103 as the treated gas 107.
FIG. 15 shows a water-flowing mechanism of a wet type electrostatic precipitator according to a conventional art. As shown in FIG. 15, in a wet type electrostatic precipitator 100, spray nozzles 108 are generally arranged above the dust-collecting plates 104 as a water-flowing mechanism, wherein the mist and dust collected on the dust-collecting plates 104 are washed away by washing liquid 110 supplied from a water supply pump 109 and injected from the spray nozzles 108. Accordingly, the collection capacity of the dust-collecting plates 104 is maintained.
However, the water-flowing mechanism in the wet type electrostatic precipitator described above has a problem such that water droplets of the washing liquid injected from the spray nozzles 108 are caught in the airflow of the gas to be treated 106, and therefore, a stable water film cannot be formed on the surface of each of the dust-collecting plates 104. In the upflow type wet type electrostatic precipitator 100 in which the gas to be treated 106 is introduced from the lower part of the casing 101 and discharged from the upper part, in particular, the upflow of the gas to be treated 106 squarely collides with the droplets of the washing liquid 110 injected from the spray nozzles 108. Therefore, the phenomenon, in which the considerable amount of the droplets of the injected washing liquid 110 are discharged from the upper part of the casing 101 with the gas to be treated 106, becomes significant, which makes it more difficult to effectively form a water film on the dust-collecting plates 104.
Japanese Patent Application Laid-Open (JP-A) Nos. 2002-224588 and 2001-190982 disclose a countermeasure for solving the problem of the water-flowing mechanism in the wet type electrostatic precipitator described above.
JP-A-2002-224588 discloses a countermeasure for solving the problem of the water-flowing mechanism in the wet type electrostatic precipitator described above. FIG. 12 is a perspective view of a water-flowing mechanism disclosed in JP-A-2002-224588, and FIG. 13 is a sectional view of a washing liquid supplying part thereof. A water holding part 2 is provided at the upper part of a dust-collecting plate 1 so as to enclose the upper end 1a of the dust-collecting plate 1. An opening part 4 whose opening width is adjustable by a blade 3 is formed at the lower end of the water holding part 2. The opening part 4 nips the upper part of the dust-collecting plate 1 with a narrow gap formed between the opening part 4 and the dust-collecting plate 1. When washing liquid is supplied from a water supplying tube 5 connected to the upper part of the water holding part 2, the washing liquid is collected in the water holding part 2, and the washing liquid flows through the gap between the opening part 4 and the surface of the dust-collecting plate 1, whereby a water film is formed on the surface of the dust-collecting plate 1.
According to the water-flowing mechanism disclosed in JP-A-2002-224588, a stable water film can be formed on the surface of the dust-collecting plate 1 while being insignificantly affected by the airflow of the gas to be treated. JP-A-2001-190982 discloses a similar water-flowing mechanism.
However, in the water-flowing mechanism disclosed in JP-A-2002-224588, when washing liquid is supplied to the empty water holding part 2 at the beginning of the operation, a plenty of washing liquid leaks from the partial gap between the opening part 4 and the dust-collecting plate 1, which means a plenty of washing liquid vigorously leaks. Therefore, there arises a problem that even if the supplying flow-rate of the washing liquid from the water supplying tube 5 is increased more than the washing liquid leaking from the gap, it takes long time to fill the water holding part 2 with the washing liquid to full capacity, and the formation of the water film on the surface of the dust-collecting plate 1 becomes very unstable until the water holding part 2 is filled with the washing liquid. Further, the function of adjusting the supplying flow-rate of the washing liquid is extremely insufficient in the water-flowing mechanism. Specifically, when the supplying flow-rate of the washing liquid from the water supplying tube 5 is decreased for some reason to be less than a lower limit value even after the water holding part 2 is filled with the washing liquid to full capacity, the water surface at the water holding part 2 is lowered, and finally, the washing liquid flows only through a partial gap, which makes it difficult to form the water film on the entire surface of the dust-collecting plate 1. The water-flowing mechanism disclosed in JP-A-2001-190982, also have the similar problems although there is a difference in the degree.